Tomography of Particle Plasmon Fields using Electron Microscopy

Anton Hörl Institute of Physics, University of Graz, Graz, Austria Georg Haberfehlner Graz Centre for Electron Microscopy, Austrian Cooperative Research, Graz, Austria Franz Schmidt Institute for Electron Microscopy and Nanoanalysis, Graz University of Technology, Graz, Austria Angelina Orthacker Graz Centre for Electron Microscopy, Austrian Cooperative Research, Graz, Austria Andreas Trügler Institute of Physics, University of Graz, Graz, Austria Gerald Kothleitner Graz Centre for Electron Microscopy, Austrian Cooperative Research, Graz, Austria Institute for Electron Microscopy and Nanoanalysis, Graz University of Technology, Graz, Austria Ulrich Hohenester Institute of Physics, University of Graz, Graz, Austria

Electron energy loss spectroscopy (EELS) and microscopy allow probing of the evanescent fields of particle plasmons with nanometer resolution. In EELS, electrons with a high kinetic energy pass by or penetrate through a metallic nanoparticle, excite particle plasmons, and lose part of their kinetic energy. By monitoring the energy loss as a function of electron beam position, one obtains detailed maps about the localized plasmonic fields [1].

Despite its success and widespread application, the interpretation of plasmonic EELS data has led to some controversy [2]. Recent work has made progress in this direction by analyzing the data in terms of a tomography scheme: for EELS maps obtained for different beam directions, one can reconstruct the plasmonic eigenmodes for sufficiently small nanoparticles [3,4].

In this paper, we show how to extract the three-dimensional plasmon fields from a sinogram of EELS maps. We develop a general tomography scheme that can be generalized for larger nanoparticles without employing the quasistatic approximation. Our approach is based on a decomposition of the Green’s tensor into modes which are reconstructed by means of compressed sensing. We demonstrate the applicability of our approach for a measurement series obtained for coupled silver nanorods, showing that the reconstructed data provide most detailed information about the 3d plasmonic field distribution.

[1] J. García de Abajo, Rev. Mod. Phys. 82, 209 (2010).

[2] J. Garcia de Abajo et al., Phys. Rev. Lett. 100, 106804 (2008); U. Hohenester et al, ibid 103, 106801 (2009).

[3] A. Hörl, A. Trügler, and U. Hohenester, Phys. Rev. Lett. 111, 086801 (2013).

[4] O. Nicoletti et al., Nature 502, 80 (2013).

anton.hoerl@uni-graz.at